Heater



Feb. 7, 1950 H. J. DE N. M coLLuM 2,496 73 HEATER Original Filed Jan.15, 1943 FU EL 5UPPLY PUMP SUPPLY Patented Feb. 7, 1950 UNITED STATESPATENT OFFICE HEATER Henry J. De N. McCollum, deceased, late of Chicage, Ill., by Thelma McCo'llum, executrix, Chicago, IlL, assignor toStewart-Warner Corpora-' tion, Chicago, 115., a corporation of VirginiaOriginal application January 15, 1943, Serial No.- 4'Z2A58. Divided andthis application Novemher 5, 1945, Serial No. 626,684

5 Claims.

The invention relates generally to aircraft heating apparatus and moreparticularly to aircraft heaters in which combustion takes place withina sealed chamber. It will be appreciated that certain features of theinvention are also applicable to heaters of other types, particularlyheaters for automobiles and other mobile equipment.

This application is a division of application Serial No. 472,458, filedJanuary 15, 1943, now Patent No. 2,427,221.

The design of aircraft heaters imposes several limitations not commonlyencountered in heating equipment generally. The equipment should be keptas light and as small as possible and should have high heat outputsince, in general, the dissipation of heat from an aircraft is greaterthan is usually the case with heated spaces of comparable size.

It is one of the objects of the present invention to provide an improvedaircraft or similar type heater which is light in weight, small in sizeand safe in operation.

A further object of the present invention is to provide a novel heaterof the above type in which there is no direct communication between thecombustion air side of the heater and the ventilating air side.

Yet another object of the present invention is to provide an improvedaircraft or like type heater which is inherently safe even though theheat exchanger should crack or burn through while the heater is inoperation.

Still another object of the present invention is to provide an improvedaircraft or similar heater which carries out the above objectives underall flight and pressure conditions and at all airplane speeds.

Other objects and advantages will appear from the following descriptionof a preferred embodiment of the invention which is illustrated in theaccompanying drawings.

In the drawings in which similar characters of reference refer tosimilar parts throughout the several views:

Fig. l is a diagrammatic View of one form of the heating apparatus whichutilizes a pressure responsive valve for controlling the ventilating airpressure in the heat exchanger. This heater is also equipped with acontrol for modulating the heat output according to demand; and

Fig. 2 is a diagrammatic view showing a modified form of the inventionin which air is supplied for combustion and for ventilating the heaterby means of a ram or scoop in the air stream.

Prior to the present invention aircraft heaters of the combustion typewere so built that a burnthrough or crack'in the heat exchanger portionof the heating apparatus would be likely to result in products ofcombustion leaking from the combustion air space into the ventilatingair, with the result that the air delivered to the cabin might becontaminated so as to render it unpleasant to the occupants and, undersome conditions, unsafe. As has been pointed out previously, one of theimportant objects of this invention is to overcome this condition by theemployment of heating apparatus so arranged that leaks in the heatexchanger portion of the apparatus result in ventilating air leakingthrough the heat exchanger to the combustion side. The result, ofcourse, is that regardless of the condition of the heat exchanger theventilating air cannot become contaminated with noxious products ofcombustion.

In general, this is accomplished by supplying the combustion side of theheater and the ventilating air side of the heater from the same source,or at least sources which vary together, so that any increase inpressure on the combustion side of the heater will be reflected by asimilar increase of pressure on the ventilating air side. In addition tothe above, the ventilating side of the heater is so arranged that thepressure drop from the point at which the pressures of the combustionair system and the ventilating air system are similar to the point wherethe ventilating air enters the heat exchanger involves relatively littlepressure drop. Also, the downstream side of the heater may be equippedwith a restrictor of one sort or another in the ventilating air to theend that the major portion of the pressure drop in the ventilating airsystem of the airplane takes place at a point downstream of the heater.

It is apparent that if the above precautions are carrieclout, theventilatin air compartment of the heater will always operate at apressure well above atmospheric. By atmospheric is meant the pressure atthe discharge point of the heater system on the ventilating air side,for instance, the aircraft cabin.

The combustion air side of the heater, on the other hand, is so arrangedthat the major portion of the pressure drop in the combustion air systemoccurs upstream of the point at which combustion takes place with theproducts of combustion flowing through passages of comparatively littlepressure drop from the point of combustion to the-exhaust outlet. Underthese conditions, it will be seen that the combustion air side of theheater system from the point of combustion onwardly is always at apressure state considerably below atmospheric and this is furtherenhanced by running the exhaust pipe through the wall of the airplaneeither in a location of low pressure or else in such manner that thedynamic effect of the air flowing over the airplane will produce asubatmospheric region at the exhaust outlet.

Referring specifically to Fig. 1 in which is illustrated an aircraftheater of simple type and the heating system is further illustratedrather diagrammatically since the invention is well adapted to this typeof illustration, the heater as shown is installed in an aircraft nacellewith a cabin supercharging blower I2 and inlet M connected theretoarranged on the engine side of the fire wall it. been shown, it will beappreciated that the inlet I 4 should be so located that exhaust gasesand other objectionable fumes from the aircraft engine are not picked upand fed to the aircraft ventilating system.

The outlet i 8- of theblower leadsto-a ventilating air duct 20 which isconnected to the ventilating air case 22 of theheater indicatedgenerally by the numeral 24. The downstream end of the heater case isconnected in turn to a ventilating air duct 26 which leadsto the spaceto be heated.

Within the casing 22 is shown a plurality of heating units 28 which maybe of the general type disclosed in the prior patent of Henry J. De N.McCollum and. Thomas F. Spackman No. 2,236,789 granted April 1, 1941.These units 28 are supplied with a combustible mixture through a pipe 30which leads to a pair of manifolds 32 connected to the combustiblemixture inlets of the several heaters. The exhaust connections on theheaters communicate with a pair of manifolds 34-which lead to an exhaustpipe 35'. The exhaust pipe should extend overboard of the airplanepreferably in a position of low pressure or in such relation to theflowing-air stream outside the airplane that a subatmospheric pressureis produced at the exhaust outlet.

Air for combustion is taken from the duct l8 through a combustionairregulator valve 38 to a combustion air pipe ww-hich leads to abalanced type carburetor 42-. The carburetor receives fuel, usually thesame fuel supplied to the engine, from the fuel supply tank :14 whichcommunicates through tubing iii to a fuel pump 48 and thence by way oftube 58 to the carburetor.

Within the carburetor, combustion air flowing from the pipe 40 is mixedwith liquid fuel delivered from the fuel supply to provide a combustiblemixture and this mixture is delivered by the carburetor to the mixturepipe 30.

Somewhat downstream of the heater is shown a thermostatic helicalbimetal element 52 which is responsive to the temperature of the air inthe ventilating duct. It is connected by Way of an arm 56 with a controlrod 58 which leads to the valve 38. The control valve 38 and the controlelement 52 are not shown indetail since devices of this general naturefor control purposes are well known. The arrangement is such that uponan increase in temperature in the ventilating air duct 26 above somepredetermined level, the bimetal element 52 will move the rod 55 so asto increase the pressure drop through the valve 38.

The result is that less air flows to the combustion side of the heaterthrough the pipe 40. Inasmuch as the combustion air rate is reduced thecarburetor supplies less fuel and therefore the heat output of theheatin system decreases, thereby Although no aircraft engine hasreducing the temperature in the ventilating air duct downstream of theheater so as to bring the system back into balance.

In order to insure a sufiicient pressure at the combustion air pipeinlet to produce sufi'icient flow through the combustion side of theheater, a pressure responsive valve is located downstream of the heater.This valve comprises a butterfly damper 58 pivoted to rotate within theduct 26 from a fully closed position, as shown, to a more wide-openposition in which it approaches an attitude more nearly parallel to thecenter line of the duct. This butterfly valve is connected by an arm(iii to a link t2 which in turn is attached to a sylphon type bellowselement St. The ventilating air pressure within the duct 26 iscommunicated to the bellows M in such manner that as the pressure risesthe bellows element will elongate, thereby pulling upon the link E2 andtending to swing the damper toward open position. As the damper opensthe pressure drop through the system decreases, thereby permitting thepressure within the duct 25 upstream of the damper to approach the cabinpressure. This decrease in pressure, of course, causes the sylphonbellows element fi l to move in the opposite direction, thereby causingthe damper 58 to tend to reclose. The damper 58' and the associatedcontrol mechanism therefore insure a sufficient pressure differentialbetween the outside air and the air at the heater to insure an adequateflow of combustion air through the valve 38, carburetor 32, and heatingunits.

From the above description it will be appreciated that at the pointwhere the valve 38 receives combustion air from the ventilating air duct18, the pressure of the combustion air and the ventilating air will beapproximately equal. Further, it is apparent that at the outlet of theheating duct 26 the pressure will be substantially atmospheric and thatsimilarly the outlet end of the exhaust pipe 36 will be atmospheric orsomewhat less depending upon whether or not the outlet of the exhaustpipe is located in a region of subatmospheric pressure. It also will beseen that the principal point of pressure drop in the ventilating airsystem occurs at the damper 58 since this damper always produces adifferential sufficient to cause combustion air to flow through thecombustion side of the heater. It follows, therefore, that the pressureon the ventilating air side within the case 22 is well above thepressure of the ventilating air in the duct Zii downstream of the damper58.

Although the ventilating air as just described flows comparativelyfreely through the heater up to the outlet thereof, the combustion airmeets with a restriction at the valve 33 and at the can buretor 42 priorto arriving at the heating, units 28. The combustible mixture pressureat the inlets to the heating units 28 is therei'ore below the pressureof the ventilating air within the case 22. The result is that if one ofthe heat exchangers of one of the units 28 should leak, the leakage willtake place from the region'of higher pressure to the region of lowerpressur or, in other words, from the ventilating air side to thecombustion air side.

In Fig. 2 is shown a modified form of the invention in which the heaterZtreceives combustion and ventilating air from aram or scoop tiiwhichextends outside the wall 68 of th aircraft and faces toward thedirection-of flight. Air entering the scoop 66 passes through a duct 69to the inlet of the casing 22 of the heater 24, the outlet or"the-heater on the ventilating air side being coniv nected to aventilating air duct 26 leading to the space to be heated.

Since normally the pressure differential between the scoop 66 and theair in the cabin will not vary over as great a range as is common withthe supercharged cabin illustrated in Fig.1, the variable restrictionillustrated by the damper 58 has been replaced by a fixed orifice plateI0 having an opening 12 therethrough for the passage of ventilating air.The orifice plate serves as a sufficient restrictor in the ventilatingsystem to insure that the pressure in the casing 22 will be well aboveatmospheric.

As in the previous embodiment of the invention, fuel is supplied from atank 44 through a tube 45 to a pump 49 which feeds a balanced carburetor42 through a pipe 50. The carburetor in turn receives air through acombustion air pipe 40 which opens into the heater case 22 in a positionupstream of the plurality of heating units 28. The outlet of thecarburetor 42 is connected by a mixture tube 30 to a pair of manifolds32 leading to th heater mixture inlets. Similarly, also the heaterexhaust outlets are connected to a pair of manifolds 34 which connect toan exhaust pipe 36 which extends overboard into an area of low pressureor into a trailing position as shown. In Fig. 2, the inlet to thecarburetor has been provided with a check valve 14 so as to preventreverse flow through the pipes 30 and 40 in the event that a startingexplosion in the heater units 28 causes a momentary pressure rise. Undernormal operating conditions the check valve '14 may not be necessary.Whether or not it is used will depend to a considerable extent upon theparticular starting characteristics of the specific heaters used.

In the arrangement of Fig. 2 as in the previous embodiment illustratedin Fig. 1, the principal restriction in the ventilating air side of thesystem occurs downstream of the heater, whereas the principalrestriction on the combustion side of the heater, that is, thecarburetor 42, occurs ahead of the heating units 28. The result is that,as in the first embodiment, the pressure on the combustion air side ofthe individual heaters 28 is less than it is on the ventilating side,thus any leakage which takes place in the heat exchangers will produce afiow of ventilating air into the combustion air rather than in thereverse direction, thereby preventing the ventilating air from becomingcontaminated by products of combustion.

Although two specific embodiments of the invention are shown, it shouldbe appreciated that the important consideration in carrying out theinvention is so to arrange the heater or heaters that the combustion airand ventilating air start flowing from a region of similar pressure,that the pressure drops in the two systems are such that combustion airreaches the point of combustion at a pressure lower than the ventilatingair zone which is separated from the combustion air only by the heaterstructure. Further, it is apparent that this condition should persistthroughout the heater, so that at any point from the zone wherecombustion starts to the point at which the combustion air flows fromthe heater, the ventilating air in the contiguous region always ismaintained at a higher pressure, so that any leakage in the burner orheat exchanger will not result in the ventilating air becomingcontaminated by the products of combustion.

Having described the invention, what is claimed as new and useful anddesired to be secured by Letters Patent of the United States is;

,,1. In-ialheatingv apparatus for airplanes and the like, thecombination of an internal combustion type heatingunit assembly, acasing surrounding said assembly, a source of air un-.

der pressure, a conduit for supplying air from said source to saidcasing, a liquid fuel and air mixing device for supplying combustiblemixture to said assembly, a conduit for supplying air from said sourceto said mixing device, an exhaust pipe for conveying the products ofcombustion from said assembly, a conduit for conveying heated air fromsaid casing to the space to be heated, and means comprising a flowrestriction in said last named conduit immediately adjacent said casing,said restriction means providing the major flow restricting element insaid conduit and being constructed and arranged to maintain the pressurein said casing above the pressure the'interior of said assembly toprevent the products of combustion from leaking into the air beingheated and to supply combustible mixture to said assembly undersubstantially all conditions of operation in the proper amount to heatthe air to the desired temperature.

2. The combination set forth in claim 1 in which the flow restrictionconsists of a valve operated by means responsive to the pressuredifference between the interior of said casing and the outside thereofto control the rate of flow of air through the conduit in which it islocated.

3. In a heating apparatus for airplanes and the like, the combination ofan internal combustion heating unit assembly, a casing surrounding saidassembly, a source of air under pressure, a fuel and air mixing devicesupplying a combustible mixture to said assembly, a conduit forsupplying air under pressure from said source to the inlet of saidcasing, a conduit connecting the outlet of said casing with the space tobe heated to convey heated air thereto, a conduit for supplying air fromsaid source to the inlet of said mixing device, a valve regulating therate of flow of air through said last named conduit, thermostatic means,responsive to the temperature of said heated air, to operate said valveto decrease the rate of flow of air therethrough when said temperatureexceeds a predetermined value, and to increase said rate of flow whensaid temperature decreases, a passage for conveying the products ofcombustion from said assembly, and means located in the outlet of saidcasing to maintain the air pressure therein above the pressure at theoutlet of said passage.

4.111 a heating system for an airplane or other conveyance having asupercharged cabin, and a blower for maintaining the air in said cabinat a higher pressure than the surroundlng atmosphere, the combination ofa casing connected to the outlet of said blower, an internal combustionoperated heat exchange means within said casing, a duct connecting saidcasing with said cabin, and means in said duct for controlling the rateof air flow through said duct to maintain the air pressure within saidcasing sufliciently greater than the pressure within said heat exchangemeans to prevent leakage of the products of combustion therefrom to theair being heated.

5. The combination of an internal combustion heating unit assembly, acasing enclosing said assembly, a passage conveying heated air from saidcasing to the space to be heated, a device for mixing fuel and air toform a com- Maori lee bustible mixture, a duct cofivyi nglcombustiblemixture from said device to said assembly, a duct conveying the productsof combustion" from said assembly, a source of air under sufficientlygreater' pressure than the outlet of said duct to:

operate said fuel and air mixing device and'saidassembly, aconduitconnecting said source with the inlet of said device, a ductfor-supplying air from said source tothe inlet of saidcas-ing, and

means responsive to the temperature of the air flowing from said casingto control therate of flow of air through said conduit.

THEBMK McCOL-LUM; Executrix of the Last Will and Testament of Henry J.De N. Mcc'ollum, deceased;

REFERENCES CITED The following references are ofrecord innthe.

file of this patent:

UNITED STATES PA'IEN'IS OTHER REFERENCES" Magazine article, Warm; airsystem heats giant plane, pages 168, 169 and 170 of: Heating Piping andAir Conditioning for- March 1939.

